LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression

Question

I\'m migrating some stuff from one mysql server to a sql server but i can\'t figure out how to make this code work:

using (var context = new Context())
{
            


        

Answer 1

If you really want to type ToString inside your query, you could write an expression tree visitor that rewrites the call to ToString with a call to the appropriate StringConvert function:

using System.Linq;
using System.Data.Entity.SqlServer;
using System.Linq.Expressions;
using static System.Linq.Expressions.Expression;
using System;

namespace ToStringRewriting {
    class ToStringRewriter : ExpressionVisitor {
        static MethodInfo stringConvertMethodInfo = typeof(SqlFunctions).GetMethods()
                 .Single(x => x.Name == "StringConvert" && x.GetParameters()[0].ParameterType == typeof(decimal?));

        protected override Expression VisitMethodCall(MethodCallExpression node) {
            var method = node.Method;
            if (method.Name=="ToString") {
                if (node.Object.GetType() == typeof(string)) { return node.Object; }
                node = Call(stringConvertMethodInfo, Convert(node.Object, typeof(decimal?));
            }
            return base.VisitMethodCall(node);
        }
    }
    class Person {
        string Name { get; set; }
        long SocialSecurityNumber { get; set; }
    }
    class Program {
        void Main() {
            Expression> expr = x => x.ToString().Length > 1;
            var rewriter = new ToStringRewriter();
            var finalExpression = rewriter.Visit(expr);
            var dcx = new MyDataContext();
            var query = dcx.Persons.Where(finalExpression);

        }
    }
}